Devices using various types of disks such as optical disks, magneto-optical disks, and flexible magnetic disks are known as disk drives. Of these, the hard disk drive (HDD) is used in many electronic devices, such as video recording and playback devices and car navigation systems, in addition to computer systems.
An HDD has a swinging actuator and a head slider supported by the actuator. The actuator is driven by a voice coil motor (VCM). Usually, the actuator has several mechanical resonance modes. Consequently, the servo system becomes unstable because of these modes, and mechanical oscillations occur at the characteristic frequencies (resonance frequencies).
The drawings referred to in this description should be understood as not being drawn to scale except if specifically noted.